1. Field of the Invention
The present invention relates to a numerical control apparatus for controlling a roll grinding machine and, more particularly, to a numerical control apparatus for controlling a roll grinding machine, capable of detecting flaws in the circumferential surface of a roll being ground and of continuing automatic grinding until all the flaws are removed from the circumferential surface of the roll.
2. Description of the Related Art
A roll grinding machine is provided with a flaw detecting means for finding flaws in a surface of a roll being ground thereon. Flaw detecting techniques include ultrasonic test methods and eddy current test methods. Known ultrasonic test methods are disclosed in, for example, JP-A No. 1994-142215 and JP-A No. 1994-281213. A known eddy current test method is disclosed in, for example, JP-A No. 1992 3-35158.
Although the relative depths and sizes of flaws formed in the circumferential surface of a roll can be determined by a conventional flaw detector, the absolute depth of each flaw cannot be determined by the conventional flaw detector.
When grinding a roll by a conventional roll grinding machine, a cycle consisting of grinding process, testing process and grinding process is repeated, in which the circumferential surface of the roll is inspected by a flaw detector, the operator visually recognizes flaws and the roll is ground in a manual grinding mode, until all the flaws disappear. Therefore, an automatic grinding process controlled by a numerical controller is not suitable for grinding a roll having flaws in its circumference and the operator must watch a grinding machine throughout a grinding process from beginning to end and hence such a roll cannot efficiently be ground.
Accordingly, it is an object of the present invention to solve problems in the prior art and to provided a numerical control apparatus for a roll grinding machine capable of automatically carrying out a series of steps including those of detecting flaws in a roll and grinding the roll, and of automatically and efficiently performing a grinding operation until all the flaws in the roll are removed.
With this object in view, the present invention provides a numerical control apparatus for the numerical control of a roll grinding machine that supports a roll to be ground between a headstock and a tailstock, rotates the roll, cross-feeds a wheel spindle stock supporting a grinding wheel in a radial direction and longitudinally feeds the wheel spindle stock supporting the grinding wheel in parallel to the axis of the roll to carry out a programmed series of grinding steps, comprising: a flaw detecting means for scanning an entire surface of the roll, provided with a flaw detecting head for detecting flaws formed in the surface of the roll; a flaw information generating means for generating flaw information specifying positions of the detected flaws; a command generating means for generating cross-feed commands to repair detected flaws on the basis of flaw information; a control means for executing a first axis position control on the basis of the cross-feed command to position the grinding wheel at a position corresponding to the position of the flaw by longitudinally moving the wheel spindle stock in parallel to the axis of the roll and a second axis positioning control to cross-feed the grinding wheel radially; a decision means for deciding whether or not the flaw has been completely repaired and providing the stop signal for cross-feed motion to the control means; and a skipping means for skipping to the next cross-feed command if the flaw has been completely repaired.
Preferably, the decision means includes a next command invoking means that compares an output signal of a flaw detector and a predetermined flaw level threshold, and decides that the flaw has been completely repaired when the output signal of the flaw detector provided while the roll turns one full turn is smaller than the flaw level threshold.